The proposed Clinical Core will identify and follow 500 patients at all stages of Alzheimer's disease (AD) and related dementing illnesses, 100 patients with mild cognitive impairment, and 300 elderly controls who come from anywhere in the state of Arizona. All subjects will undergo a diagnostic battery of tests providing information and data from demographic, historical, medical, neurological, psychiatric, and neuropsychological measures. Based on strict entrance criteria, eligible patients will be discussed in a diagnostic consensus conference and then offered enrollment in the research center. Enrolled research subjects will undergo apolipoprotein E (APOE) genotyping, and a standard neuropsychological battery, which will be administered at all clinical sites to all patient and control subjects. The enrollees will be screened for potential participation in ongoing and developing research projects involving brain imaging, neuropathology, neuropsychology, natural history of aging and dementia, genetics of disease, therapeutic trials, and predictive modeling. All will be enrolled in the brain donation program for neuropathological confirmation of clinical diagnoses. The proposed Clinical Core capitalizes on several unique strengths that enhance our feasibility for achieving our patient recruitment goals, including a large catchment area represented by all the major tertiary care referral centers throughout the state of Arizona, the availability of existing cohorts of longitudinally studied dementia patients and age matched controls already committed to participation in our brain bank program, regional access to Hispanic and Native American populations through community outreach and educational services, availability of an existing cohort of cognitively normal individuals at genetic risk for AD with the APOE 4 genotype from a separately-funded ongoing longitudinal study, and demonstrated expertise in the diagnosis and clinical study of patients with dementia syndromes and mild cognitive impairment.